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Port Jackson Shark
The Port Jackson shark (Heterodontus portusjacksoni) is the largest of the Heterodontid sharks. It is one of the three Australian species within its eight-member family (Heterodontidae, the Bullhead and Horn Sharks), along with theCrested Bullhead and Zebra Bullhead. Adults can grow up to 1.65 m (5.4 ft) long, although the typical length is more like 75 cm (2.5 ft) for males and 90 cm (3 ft) for females. This common bottom-dweller is named for Port Jackson, the famed and stunning natural harbor of Sydney, Australia. It is also sometimes called the “Oyster Crusher”. It is a distinctive species that is pretty much impossible to misidentify. Like all Heterodontids, it has a blunt-shaped head and spines on the leading edge of the two dorsal fins. However, the Port Jackson shark has a unique color pattern of a light background with dark, harness-like markings that cover the eyes, run along the back to the first dorsal fin, and then cross the side of the body. When viewed head on (as seen below), this shark has a bizarre, alien look enhanced by the unusual mouth and arched ridges over the eyes. Description The dorsal fins’ spines are thought to be the source of one of the family’s common names, “Horn sharks”. According to many on-line sources, these spines are reputed to be venomous. It sounded fishy to us (pun intended), and we could not find reliable support of the claim – in fact, one resource from the University of Michigan said that they are NOT venomous. The spines of juveniles can be quite sharp, but they become duller with age. Spines wash up beaches, and have reportedly been confused for objects from bird beaks to goat horns. Biology This species can eat and breathe at the same time, an unusual ability because most sharks must swim open-mouthed to force water over their gills, in order to obtain oxygen. In contrast, the Port Jackson shark can actually pump water through its gills, while stationary. Much is known about the biology and ecosystem roles of this species compared to many sharks, because it is common and well-studied. For example, many ectoparasites (the kind that attach to the outside of the body) have been identified on Port Jackson sharks, including marine isopod Habitat and Range The distribution of the Port Jackson shark covers the tropical marine waters of southern Australian, from south Queensland to Tasmania, and west to the central coast of Western Australia. Genetic evidence indicates the possibility of two distinct populations. This species is found in depths from 100 to 275 m (330 to 900 ft). The preferred habitat is rocky, sandy or muddy substrates on or near the ocean bottom, and also areas where seagrass grows. During the day, it often rests in the protected shelter of caves and crevices of rocky areas. The Port Jackson shark is sympatric with the less common Crested Bullhead (H. galeatus). They can be found in the same habitat throughout much of the bullhead’s range, with the bullhead gradually becoming more common in northern/warmer waters compared to H. portusjacksoni. Feeding Behavior This is a nocturnal shark that feeds at night when their prey species are most active. The diet consists mainly of sea urchins. Prey items also include small fish, and benthic invertebrates such as sea stars, polychaete worms, gastropods, prawns, crabs and small fish. Unlike the “classic” shark teeth that are large and sharp, perfect for eating meat, the teeth of Bullhead and Horn sharks are adapted for their diet of shelled creatures. They actually have two kinds of teeth: the front ones are small and pointy for grabbing and holding prey items, while the broad, flat back teeth are like molars, used for crushing and grinding shells. Immatures feed on more soft-bodied prey than adults, and correspondingly they have more pointed teeth. The young sharks can feed by sucking in water and sand from the bottom, blowing the sand out of the gill slits, and retaining the food which is swallowed. Social Behavior This species forms large aggregations of both mixed and same sex groups, as described below regarding reproduction. Breeding Female Port Jackson sharks become reproductively mature at 11 to 14 years of age, while males need only 8 to 10 years to reach maturity. Breeding occurs only once a year for this species. Normally males and females are segregated, using different habitats for most parts of the year. They share the same space only briefly, during the mating season. Both sexes move into inshore reef areas in July. Mating occurs during the austral winter in July and August. In that period, divers frequently spot sharks congregating in caves and under rocky ledges, although the actual breeding process has never been observed. Individuals are able to stay on the sea bottom for long periods due to their ability to breathe while immobile, another behavior that is commonly observed at this time. The breeding system is oviparous – the egg case is a dark brown, spiral-shaped structure about 7 x 15 cm (2.8 x 7″) in size. A female lays about 10 to 16 of them, in shallow reefs normally at depths of about 5 m (16 ft) but up to 30 m (100 ft) deep. This happens in August and September. Females usually use the same sites year after year. The mother uses her mouth to wedge the soft case into a rock crevice, where it can harden in safety. Males move into deeper water right after breeding, followed by females after egg laying. Some individuals will stay offshore, while others undertake a southward migration after mating, traveling up to 850 km (530 mi) from their breeding reefs. They are believed to travel closer to shore through coastal waters on the southern move, and then back through deeper offshore waters when returning north to the breeding grounds. Individuals will return to the same breeding sites each year. The eggs hatch after ten to twelve months. A single pup emerges from each case and they are about 25 cm (10″) long. The empty cases are often found washed-up on beaches, where they are known as “mermaids purses”. Juveniles typically remain in the bays and estuaries of their nursery areas until close to maturity. Thus, the sharks stay in mixed-sex groups for several years, and then eventually move into deeper waters to separate into female and male groups. Humans and Conservation Port Jackson sharks are considered to pose no real threat to people, although they can inflict a nasty bite. The sharp spines of the dorsal fin can also be a danger when the species is handled. They are caught commonly in the gillnet fisheries of southern Australia, and sometimes are the most numerous species found in catches. However, the numbers taken a bycatchare unknown because there is no distinction in fishing records between this species and H. galeatus. There is no commercial interest in Port Jackson sharks as their meat and fins are considered to be poor quality. Most are discarded, often alive, while some people consider them a pest and kill them before tossing them. Recreational fishers also catch a small number of these sharks. This is one of the Heterodontus species that is commonly kept in captivity, as they are quite hardy. Small individuals are sold domestically and internationally for use in home aquaria. They are also collected for display in public facilities, but in smaller numbers. Large aquaria have been able to breed Port Jackson sharks in captivity. This shark is not considered as threatened. Populations appear to be healthy, despite fishing activities. There is a bag limit in Western Australia (four of any species per recreational trip) and fish collectors have to be licensed, but otherwise no specific management actions are in place for this species. The IUCN Red List labels it a species of Least Concern, because it appears to be abundant and there is no evidence of threat, from fishing or environmental factors. Category:Fish Category:Saltwater Fish Category:Sharks Category:Sea Creatures Category:Australian Animals Category:Predators Category:Carnivores Category:Nocturnal Creatures